General Home Automation Help Installing Speaker Volume Controls ...

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Subject Author Date
Help Installing Speaker Volume Controls ... M100C 12-24-05
Posted by M100C on December 24, 2005, 10:22 am
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All,
I need some help understanding how volume control impedance calculates into
the load seen by the amplifier. Here is my scenario, using just one amp
channel for illustration purposes:

I have an amp rated to drive loads from 6 to 16 ohms ... ideally, I would
like to present the amp with an 8 ohm load.

I have three, 8 ohm speakers, all with home runs back to the amp. When
connected in parallel, they will provide this channel with a load of 2 2/3
ohms (1/Rt = 1/8 + 1/8 + 1/8), which is clearly too low.

This is where I start to get a little fuzzy about how the volume control
impedance works ... I know need to create another 6 ohms of impedance to
bring the total impedance for this channel to just over 8 ohms, but here are
my questions:

1) Are I seeing this correctly? If so, I have not been able to identify any
volume controls which would create the proper "make-up" impedance. Your
suggestions are welcome.
2) Ideally, I'd like to have a volume control with an "off" setting. In
this case, I assume that there might be a make-break switch which removes
the speaker from the circuit and adds the additional impedance needed to
replace the speaker ... is this correct?

Thanks for the education,

Chris



Posted by on December 25, 2005, 4:33 am
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Most impedance matching volume controls have a selectable impedance
multiplier. If you were to select "4X" on each of your VC's you'd have
1/Rt = 1/32 + 1/32 + 1/32 which is 10-2/3 Ohms and safe for your
amplifier. Selecting "2X" on all three would yield a net impedance of
5-1/3 Ohms, too low for the amp.

But wait... If you have one room that is larger / needs more volume
than the other two. You could set that room for "2X" and the other two
rooms for "4X". The result would be 1/Rt = 1/32 + 1/32 + 1/16, which
is exactly 8 Ohms.

The Russound V/C's I carry have an off position. The side of the
autoformer connected to the speakers becomes an open circuit. The
other side stays in the circuit, but draws virtually no power from the
line side because at that point there's nothing on the load side.

Regards,
Robert L Bass
www.BassBurglarAlarms.com


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